The present invention relates to optical scanning systems and more particularly to optical scanning systems adapted for use in point of sale (POS) applications where articles bearing coded labels or tags can be automatically read at a scanning station.
The present state-of-the-art of POS techniques has advanced to the point where several approaches have been proposed for automatically reading a label or tag associated with a sale article. The coded information on the label may include such data as the type of article, price, stock number, name of manufacturer, and the like. Obviously, in a retail store situation, any system having the capability of extracting data of this type not only has the advantages of accelerating the flow of checkstand traffic and reducing operator errors but can also provide constantly updated data concerning inventory and sales volume as well as providing the customer a fully itemized sales receipt.
Most recently, in the retail grocery trade, articles are being marked at the source by the manufacturer with a coded label conforming to an industry specification known as the Universal Product Code (UPC). This coded label contains data relating to the name of the manufacturer as well as a catalog or inventory number identifying the particular product. A so-called back room computer addressed by the scanner-decoded manufacturer and product inventory number is capable of looking up the current price as well as current inventory information and making the same available at the checkstand terminal. Such information may be printed on the customer's sales receipt or otherwise made available to supervisory personnel thereby providing continually updated information.
Of the several techniques proposed thus far, all suffer from one or more drawbacks. For instance, an article may bear its associated coded label on the top or bottom or any one of its sides. With known techniques, as the article approaches the scanning area, the checkstand operator must orient the article so that the label faces the scanning slot--otherwise the scanner is unable to scan the label.
Such known techniques also have stringent optical requirements necessitating specially designed optical components such as high precision, unusual configuration lenses and prisms. Needless to say, these components are extremely expensive to manufacture and to align properly within the equipment during assembly and subsequent maintenance.
A further drawback includes the complex scanning pattern necessary to prior art proposals. Typical scanning patterns include Lissajous, multiple-H's and multiple sine curves. These patterns are not only difficult to generate but, since the velocity of the scanning beam in some cases is not constant, the sensed information may be difficult to decode.
In addition, conventional equipment employ sensing techniques which are not truly retro-reflective. That is, the sensor is incapable of viewing only the spot illuminated by the scanning beam but actually views a much larger area. This results in the requirement, in the prior art, for large area sensors and high light levels together with the problem of saturation of the sensor by ambient light pickup.
Prior art systems also require the use of glass plates to cover the scanning slots. This is due to the complex configurations of known scanning patterns which make an open slot arrangement mechanically impossible. The glass plate is subject to scratching as articles are passed over it during scanning operation and must frequently be replaced since the scratched glass curtails the pickup response of the sensor. In addition, products or articles containing a high degree of debris such as produce or which are subject to leakage in the case of meat and dairy products will soil or cloud the glass necessitating frequent cleaning.